I laugh at myself but this worked out really well - I shaved down the cracked portion of the original panel and created a new back plate with .. the screw top from two liter coke bottles. They required a touch of trimming to fit well. I used Gorilla Glue to laminate them to the back shell.

The only trick is to control the glue so you do not end up with a mess on the visual side. These caps are the perfect toughness for the application and the finished product is factory in its appearance.